Exemplary embodiments of the present invention relate to a multi-screen video playback system suitable as a video playback device in a large multi-screen display, and the like, to a video playback method in a multi-screen video playback system, to a timing server, a video distribution server V and a rendering unit used in a multi-screen video playback system, and to a display device to constitute a multi-screen display.
FIG. 30 is a schematic showing a multi-screen display. This multi-screen display D is a display device which constitutes one large screen by combining a plurality of display devices D1 through D4, such as a monitor and a projector, as shown in FIG. 30. The multi-screen video playback system is a video playback device to output a video signal which is inputted to each of the display devices D1 through D4, respectively, in such a multi-screen display D.
In this multi-screen video playback system, as disclosed in the related art, a large screen display is realized, by converting a video signal (a video signal corresponding to the original video (a video signal)) corresponding to a large screen, to each video signal (each video signal corresponding to each unit video (a video signal)) corresponding to each of the display devices D1 through D4 using a scan converter, and by inputting each of these video signals to each of the display devices D1 through D4.
In the related art, the digitization of a video signal has progressed. Further, a demand of wanting to handle the video signal in a digital signal format is also increasing in such multi-screen video playback system.
However, when handling a video signal in a digital signal format this way, since, unlike the case where the scan converter is used, the video signal cannot be automatically synchronized between each of the display devices D1 through D4, it is necessary to provide some synchronized playback device to establish synchronization of the video signal.
Namely, when providing such synchronized playback device, because it is possible to establish synchronization of the video signal between each of the display devices D1 through D4, a unit video, which each of the display devices displays respectively, can be reproduced at right timing, as shown in FIG. 31a. Accordingly, a smooth and natural video can be reproduced as a whole screen, while not providing the synchronized playback device such as the above one. That is, it is difficult to establish synchronization of the video signal between each of the display devices D1 through D4, the unit video which each of the display devices displays respectively is no longer reproduced at right timing, and it is impossible to reproduce a smooth and natural video, as the whole screen, as shown in FIG. 31b. 
Japanese Laid Open Patent Publication No. 2002-369163 and “3D Interactive Processor for 3D moving images”, Takaaki Kudo, and Yasuhiro Takaki; Proceedings of 3D Image Conference 2003; and Executive Committee of 3D Image Conference 2003, PP 125-128 (hereinafter “Kudo”) disclose synchronized playback devices to establish synchronization of a plurality of video display, or for establishing synchronization of video and audio, this way.
FIG. 32 is a schematic showing the synchronized playback device disclosed in Japanese Laid Open Patent Publication No. 2002-369163. In the synchronized playback device disclosed in Japanese Laid Open Patent Publication No. 2002-369163, as shown in this FIG. 32, when transmitting a plurality of video signals and the like (a stream) through the Internet, the synchronization of the video signal and the like between each display device is established by absorbing the fluctuation of time produced due to the congestion conditions of a network 9 from a transmission side system shown in FIG. 32a to a receiving side system shown in 32b of this view, and the variation and the like of the processing time required for the compression and the expansion of streams 1 and 2.
Namely, in the transmission side system, a time code at the time of distribution is attached to a plurality of streams to be distributed, and is sent out to the network. In the receiving side system, a plurality of streams are received at a plurality of receiving devices 11 and 14, respectively, to output as a stream. Then, regarding each outputted stream, the difference between a time code of the absolute reference time at the receiving side system and a distribution time code attached to the stream is measured, and the output delay of each stream is controlled so as to set the difference of each time code of each stream to be constant. Thus, the synchronization of the video signal and the like is established between each display device.
FIG. 33 is a schematic showing the synchronized playback device disclosed in Kudo. In the synchronized playback device disclosed in Kudo, as shown in FIG. 33, by connecting a host PC which generates the video playback timing to each cluster PC (PC1, PC2, PC3, . . . , PCN) which outputs each video signal (video 1, video 2, video 3, . . . , video N) to each display device by LAN (Local Area Network), and by distributing simultaneously a broadcast packet as the synchronized signal from a host PC to each PC, the synchronization of the video signal between each display device is established. Consequently, it is possible to suppress the deviation of frame between each display device to less than one frame.
Moreover, Japanese Laid Open Patent Publication No. 2003-235027 discloses a technique to establish synchronization between each display device.
When a plurality of members receive and reproduce a common video data from a distribution server in a plurality of terminal devices, if there is produced a deviation in the receiving time at each terminal device, the scene viewed and listened to at each terminal device will deviate and an inconvenience will occur in the communication between each member. Therefore, Japanese Laid Open Patent Publication No. 2003-235027 discloses a technique which ensures the synchronization of the video playback in a plurality of terminal devices in order to reduce or prevent this.
In Japanese Laid Open Patent Publication No. 2003-235027, first, the time of the video distribution server and each terminal device is unified by a time distribution server which exists on the network. Next, the video distribution server distributes a multicast packet including the video data and the information that indicates the distribution time to each terminal device. Each terminal device receives the distributed multicast packet, and by distributing the information regarding the transmission time and the receiving time to any one terminal device, the information on the difference of receiving time is collected to one place. Then, the maximum transmission delay time is calculated from this time information, and on the basis of this time, a playback timing control section of each terminal device adjusts the playback timing of the video data, and thereby, the synchronization is secured.